1. Field of the Invention
The present invention relates to improved compositions comprising organosiloxanes and epoxy compounds. In one aspect the invention relates to novel curable compositions. In another aspect the invention relates to improved molding compounds.
2. Description of the Prior Art
The desirability of curable silicone composition and curable epoxy compositions as encapsulating materials for devices, especially for electrical and electronic devices, has been appreciated for a long time. However, certain of these compositions have deficiencies such as lack of abrasion resistance, poor resistance to moisture and/or heat, excessive brittleness and inferior electrical properties. In an attempt to avoid one or more of these deficiencies silicone-epoxy compositions have been prepared and disclosed. Of particular interest are the essentially anhydrous compositions described by Bank, et al. in U.S. Pat. No. 3,971,747.
The compositions of Bank, et al. are particularly useful as the binder resin in molding compositions. However, when electronic devices are enclosed with said molding compositions, for example as in a transfer molding process, leaving wire leads protruding from the cured molding composition, there is a tendency for water to "wick" up the lead. Under certain conditions, this wicking can interfere with the proper operation of the enclosed device.
One method of decreasing this wicking is commonly known as backfilling and comprises treating the encapsulated device under reduced pressure with a fluid, curable composition which will enter the microcracks and openings of the cured molding composition when the pressure is returned to normal. This method constitutes an extra step in the process of preparing encapsulated devices and adds to the cost of the device. A more economical method of reducing wicking is desired.